What a mess! The kids in Ms. Frizzle's class have been studying animals' homes. There's a beehive, a wasp's nest, an ant farm — even a beaver lodge right in the classroom. It's a relief when the Friz announces, "Today we start something new." They are going to study earth science. For homework, the kids are supposed to bring in rocks. But when they show up with everything from concrete to muddy Styrofoam, Ms. Frizzle decides it's time for a field trip. All aboard the Magic School Bus! The class digs through the earth's crust, then travels straight to the center of the earth and out the other side — through the mouth of a volcano! Rock collecting has never been quite like this!